This application generally relates to packet-switched telephony networks, such as IP telephony networks, and to cellular networks, and more particularly to a technique that allows subscribers to roam between an IP-telephony network and a cellular network.
IP-Telephony Networks
Voice or telephony services can now be provided over a packet-switched network, such as the Internet. These packet-switched-telephony networks are commonly referred to as IP telephony networks because the Internet Protocol (IP) is the primary protocol used over the Internet. One IP telephony standard, for example, is the International Telecommunications Union (ITU) H.323 standard.
FIG. 1 illustrates an example of an IP telephony network, also known as a Voice over IP (VoIP) Network. The VoIP network includes a gatekeeper function, one or more gateways and a packet-switched network (e.g., a portion of the Internet).
The gatekeeper function is optional and provides call authorization for both accepting and placing calls in its zone or area of control. A gatekeeper can also allocate bandwidth, can maintain call detail records, and can perform other network management functions.
A packet-switched-telephony gateway bridges a circuit switched network such as the Public Switched Telephone Network (PSTN) and a packet-switched network such as an IP network or the Internet. The (standard) IP telephony gateway bridges the PSTN and IP networks to allow phone-to-phone and phone-to-personal computer (PC) multimedia communications (voice, video and/or data). The IP telephony gateway provides the appropriate translation between transmission formats (for example, H.225.0 of an H.323 endpoint to/from H.221 of an H.320 endpoint) and between communication procedures (for example, H.245 of an H.323 endpoint to/from H.242 of an H.320 endpoint). The IP telephony gateway also performs call setup and clearing on both the network side and the switched circuit network side. Translation between video, audio, and data formats may also be performed in the gateway. In general, the purpose of the IP-telephony gateway is to complete the call in both directions between the network endpoint and the switched circuit network endpoint in a transparent fashion.
An example of IP telephony gateway is the H.323 gateway (implementing the ITU H.323 standard). H.323 gateways allow interoperation of H.323 systems with other audio/video conferencing systems on Integrated Services Digital Networks (ISDN), plain old telephone systems (POTS), Asynchronous Transfer Mode (ATM), and other transports. An IP telephony gateway operates as an endpoint on the IP-telephony network that provides real-time, two-way communication between IP telephony terminals on the IP-based network and other ITU terminals on a switched-circuit network, or to another IP-telephony gateway. Switched Circuit Network connectivity is achieved in the IP telephony context by using gateways for H.320 (ISDN), H.324, H.323, POTS, and other endpoints on other networks.
FIG. 1 is a diagram illustrating an example IP telephony network. Referring to FIG. 1, when an incoming call (1) reaches an IP telephony gateway (GW) (here indicated as Originating IP telephony GW), the gateway contacts the gatekeeper it is registered with asking to set up a call towards the dialed number received from the incoming call set up request (Access Request, ARQ, 2). The gatekeeper translates the dialed number (or directory number) into the IP address of the Destination IP-telephony gateway, i.e. the gateway that has to be reached in order to reach the final destination of the call, and provides this IP address to the originating IP telephony gateway (Access Confirmation, ACF, 3). The Originating IP-telephony GW sets up an IP-telephony call over the packet-switched network or IP network towards the Destination IP-Telephony GW providing its IP address and the dialed number (Call setup, 3). The Destination IP-telephony GW contacts the gatekeeper it is registered with (it may be the same as the Originating IP-telephony GW or a different gatekeeper) asking to accept a call incoming from the Originating IP-telephony GW (ARQ, 4) and directed towards the dialed number. If the gatekeeper grants the incoming call to the Destination IP-telephony GW (ACF, 5), the Destination IP-telephony GW establishes the PSTN call (call, 7), and then the call is established between the two IP-telephony GWs over the IP network (call establishment, 6). The destination IP-telephony gateway translates the IP packets into the appropriate format for transmission over the PSTN.
However, IP telephony standards and products are currently defined only for fixed networks. Mobility has not been considered in IP telephony in the sense that IP telephony subscribers are not allowed to roam between IP telephony networks.
For example, a subscriber in one area of the country is registered with a local gatekeeper. If the subscriber moves or travels to another part of the country, the subscriber will not be able to connect to the gatekeeper in the new part of the country because the new gatekeeper has no information describing the subscriber.
Cellular Networks
In addition, cellular subscribers can roam within cellular communication systems. In Global System for Mobile (GSM), a visiting location register (VLR) and a home location register (HLR) are used. The VLR contains relevant data of all mobile stations currently located in a serving Mobile Services Switching Center (MSC). The HLR is a database in charge of the management of the mobile subscribers. The data stored in the HLR includes service subscription information and location information (the identity of the currently serving VLR to enable routing of mobile-terminated calls).
When a visiting (or roaming) cellular subscriber is detected in a serving system, the location update processes notify the subscriber's HLR of the subscriber's presence in the serving system. When the subscriber is detected for the first time, the serving system creates a temporary record for the subscriber storing the service information and the location information. When the subscriber changes serving areas, the record in the HLR is simply updated with the new location information. In both cases the HLR is notified. When the HLR is notified by the serving system, it updates the location information in the subscriber's record. If the location information is different from the one previously stored in the record, the HLR cancels the subscriber's location in the previous serving system.
If subscriber B is roaming in a serving cellular system and a party A dials subscriber B's directory number, the call is routed through the PSTN to the home system of subscriber B. The MSC in the home system that receives the incoming call contacts subscriber B's HLR to determine how to route the call. The HLR determines that the call is for subscriber B and issues a request to subscriber B's current serving system for the information to route the call. The serving system allocates a telephone number (often called Roaming Number or RN) temporarily assigned to subscriber B to route the call and provides the RN to the HLR. The HLR provides the RN to the MSC in the home system, which in turn routes the call to the RN through PSTN. When the serving system receives the incoming call, it associates it with subscriber B based on the RN, and pages the subscriber B.
However, IP-telephony networks presently do not permit roaming or mobility within the IP-telephony network. Also, cellular networks and IP-telephony networks are distinct and incompatible networks and do not allow for roaming between cellular and IP-telephony networks.
Short Message Service (SMS)
As provided in Global System For Mobile Communications (GSM), Short Message Service (SMS) gives cellular network subscribers the ability to send and receive short text messages. Short messages usually contain about one page of text or less. Some systems limit the short message to 160 alphanumeric characters. However, there is presently no provision for delivering short messages over an IP-telephony network, or for delivering short messages to subscribers roaming between a cellular network and an IP-telephony network.
Therefore, a need exists for a technique that allows subscribers to roam within an IP-telephony network, to roam between an IP telephony network and a cellular network, and for the delivery of short messages over an IP-telephony network.